Thirty years ago, Springfield has a town meeting where a younger version of the Old Jewish Man mentions that Springfield's Soviet sister city Springograd has "disappeared from the map." Afterwards, a younger Hans Moleman was shown to be the Mayor of Springfield when he reveals Springfield's new anthem "Only Springfield." The anthem is played by Dewey Largo on the piano with the song being sung over the years.
At the latest town hall meeting in the present where "Only Springfield" was being performed, Moe returns from his vacation in Tuscaloosa, Alabama and stops the singing of the anthem. Besides describing his vacation, Moe shows Tuscaloosa's anthem on MyTube to the citizens where it is the same as their anthem which caused various reactions from the citizens like Dewey Largo pushing the piano off the stage, Kirk and Luann Van Houten spilling the drinks and stepping on the cups, and the Rich Texan wonders what to do with guns when a person is angry. When Sideshow Mel claims it to be an amazing musical coincidence, Moe then shows the anthems on MyTube where the cities that used the generic anthem outside of Tuscaloosa have included but are not limited to Austin, Texas, Oakland, California, Calgary, Provo, Utah, Ulan Bator (their anthem is sung by four Mongols), and Area 51 (their anthem is sung by a guard and three aliens). Moe states that every town has their own version of the same anthem including Des Moines, Iowa. Mayor Quimby identifies that the song was written by former mayor Hans Moleman as the citizens converge on him. Hans admitted that he bought the anthem from a salesman that's been selling it to half the towns in North America and stated that he didn't think anyone would find out since he thought nobody goes anywhere outside of Springfield. Groundskeeper Willie states that he can't do away with the anthem's lyrics on his chest and that he'll never be buried in a Jewish cemetery. When Hans Moleman begs for mercy, the citizens tie up Hans Moleman and put him on a horse which gallops into the desert. Lisa says to Mayor Quimby that she could write a new anthem. Pharrell Williams shows up and says that he could also write one. Mayor Quimby states that Lisa offered to write one first and Pharrell starts to recite his song "Happy." The citizens then give Pharrell the same punishment as Moleman where Pharrell shouts "Shelbyville Rules, Springfield Drooools!!"
Lisa and Bart compose a new anthem called "Why Springfield, Why Not" and perform it with the other students. Homer has difficulty sitting in his seat at the performance due to his obesity. When he must stand to give a standing ovation, he tears out his row of seats, causing destruction to the theater. Marge demands that he joins a weight-control group, but the one he joins run by the mobility scooter-bound Albert states that obesity is beautiful. They cause a disruption outside a fashion store which they claim promotes unrealistically thin figures and all are arrested.
Marge arrives to bail Homer on condition that he leave the group and start a diet, but he refuses and returns to jail with his obese friends. Lisa and Bart try to compose a song to convince Homer to leave the group, but argue so much that they never perform it. Marge points out that Homer should not follow Albert, who she says is too lazy to walk. He attempts to get up from his scooter to prove her wrong, but suffers a fatal heart attack.
At the funeral, Albert was shown to have been cremated and his ashes were stored in a bunch of jars. Homer delivers a eulogy where on learning that the deceased was only 23, pleads for the obese people to lose weight. He and Marge walk home as he promises to yo-yo diet, and a montage shows Homer's physique changing drastically with his age.
In the final scene, Hans Moleman is still being galloped into the desert as he finally says "Whoa" to stop the horse. He then comments that he should have done that in the first place.